Devices apparently comparable to that of this invention are known in this field. Among the most interesting documents we can cite for instance those reported in the following documents: WO 9218178, EP-A 0206971, U.S. Pat. No. 3,994,296, FR-A 2262535, DE-U 9003505, FR-A 1551012.
Nevertheless none of them succeeded in solving the most important problems related to this kind of device, such as for instance:
1) a perfect sealing of the stopper-plunger, ensuring a good sliding capacity; PA1 2) a perfect coupling system of the two components which is both simple (for instance the screw type is excluded) and efficient in order to allow the possible sliding back of the piston-container during the use, when needed; PA1 3) the need of avoiding that the sharp end of the housing-barrel collecting system (the collecting needle tip) accidentally comes into contact with the operator.
In particular WO 9218178, which suggests one of the simplest and most interesting solution, was not able to solve points 1) and 2) in an acceptable way.